1. Field of the Invention
The present invention relates to a self-priming chemical pump.
2. Description of the Related Art
Heretofore, there are few cases where centrifugal volute type chemical pumps are made of metal but there are most cases where they are made of plastics, because they are adapted to medical fluids strong in chemical activity. This type of chemical pump disposed on a medical fluid tank becomes unable to pump a fluid when air is mixed in the fluid in a period in which the pump operates. In this occasion, the pump is unable to the liquid unless air escapes and plastics will be deformed by friction heat to cause serious accidents if the pump runs idle. A self-priming chemical pump can be used so that air escaping can be achieved by a self-priming remaining fluid. In this occasion, a check valve is operated so that the self-priming fluid remains in the inside of the self-priming chemical pump. In the next operation of the pump, air in the pump is discharged by the self-priming remaining fluid to form a negative pressure state in the pump to thereby suck the medical fluid in the suction piping to perform a steady-state operation. In the self-priming chemical pump of the type in which the self-priming remaining fluid is secured by operating the check valve, however, solid matter may be disposed on the seal surface of the check valve in the case of a crystalline fluid or a slurry fluid so that the check valve cannot be closed. As a result, the fluid in the pump may be made to escape from the inside of the pump so that no self-priming fluid remains in the pump. In this occasion, the pump runs idle when the next running of the pump is started. This may cause serious accidents.
From this point of view, the Applicant of the present application has developed a valveless self-priming pump (see Japanese Utility Model Postexamination Publication No. 2322/1976). This self-priming pump comprises a self-priming chamber communicating with the discharge side of an impeller, and a suction chamber communicating with the suction side of the impeller. The suction chamber is separated, by a separation wall having communication pores at its upper and lower portions, into a portion directly communicating with a suction opening and a portion not directly communicating with the suction opening. When the operation of the pump is stopped, the fluid is siphon-cut so as to remain both in the self-priming chamber and in the suction chamber. The fluid reserved in the portion not directly communicating with the suction opening returns slowly to the portion directly communicating with the suction opening through the above-mentioned pores at the lower portion of the self-priming chamber, so that a large quantity of the self-priming remaining fluid can be reserved.
In the above self-priming pump proposed by the Applicant of the present application, not only siphon-cutting is performed easily but also the volume of the suction chamber is large though the pump is of a valveless type, so that a large quantity of the self-priming fluid can remain. Accordingly, the above pump is excellent in the point of view that self-priming characteristic can be fulfilled sufficiently. In the above pump, however, a circulation hole a provided between the self-priming chamber and the vortex chamber is located outside the outer circumference of the impeller b as shown in FIG. 15. Accordingly, because the fluid blown out from the circulation hole a serves to push back the fluid which remains in the vortex chamber c and which is urged to move outward by the impeller b, these fluids are mixed with each other in the vortex chamber c. Accordingly, air moves slowly, so that the magnitude of negative pressure at the center portion of the impeller p cannot be made large rapidly. Accordingly, the self-priming speed is made slow. Further, because the gap between the vortex c and the impeller b is sufficiently large, the fluid and air contained in the fluid are made to rotate in the vortex chamber c. Accordingly, the air does not go out to the discharge side of the vortex c rapidly, so that the centrifugal action by the impeller b is weakened. Accordingly, the magnitude of the negative pressure at the center portion of the impeller b cannot be made large rapidly. Accordingly, the self-priming speed is made slow. Particularly in the case of a high-temperature fluid or a fluid containing bubbles, the influence thereof is remarkable so that there is a risk of shortage of self-priming characteristic.
Further, because the portion directly communicating with the suction opening is L-shaped, siphon-cutting is made later so that a larger quantity of self-priming fluid than required is taken in the suction piping.